This invention relates to a breakerless ignition system for internal combustion engines which detects ignition timing in response to a variation in the condition of oscillation of a resonant circuit composed of a capacitor and a coil which is wound on a core disposed in confronting relation to a signal rotor.
With prior art ignition systems of this type, noise signals are sometimes induced in the detector coil of the resonant circuit by extraneous electromagnetic radiations generated by the spark plug firings, and the intensity of the resonant oscillations is increased by the energy of such induced noise signals. As a consequence, a threshold detector coupled to the resonant circuit may produce spurious output signals which temporarily switch on a power transistor connected in series with the ignition coil, whereby erroneous firing pulses are developed in the secondary winding of the coil and the voltage and energy outputs of the latter are generally decreased.